Calibration of the Egret High-Energy Gamma-Ray Telescope in the Range 20-10,000 MeV with a Tunable Beam of Quasi-Monoenergetic Gamma Rays at SLAC

The EGRET telescope, one of the instruments to be carried on NASA's Gamma Ray Observatory, is designed to explore the high-energy portion (20 - 24,000 MeV) of the electromagnetic spectrum. A calibration source of γ-rays over this wide energy range has been used at SLAC, together with an appropriate set of intensity-monitoring instruments, to conduct a calibration of the EGRET telescope over this energy range for the full telescope aperture. The calibration method and an overview of the results are described.